The present invention relates generally to devices for pressure testing sections of pipe to identify and to quantify leakage, and specifically relates to such devices which are designed for pneumatically testing pipe sections equipped with expansion bellows.
Metallic expansion bellows are used on piping penetrations of containment drywells in many nuclear power plants as part of the containment insolation scheme. Typical bellows construction is of stainless steel and is two-ply, with a small annulus or gap between the inner and outer piles. This annulus is intended to permit periodic pressure testing for leak quantification. In nuclear power plants, metallic expansion bellows provide flexible attachment points fore process pipes in fluid communication with containment drywells. The purpose of these bellows is to accommodate relative motion between the process pipes and the containment vessel resulting from thermal expansion and pressure displacement. These conditions may occur during normal operation, as well as during accident conditions.
Although the overall performance of flexible metallic bellows penetrations has appeared to be acceptable for approximately 20 years, degradation of these components has been recently has been recently identified. Also, recently discovered deficiencies in the conventional pressure test scenario have caused concern as to the inability of regulators to accurately quantify the rate of leakage from a cracked bellows.
Conventional bellows leak rate follow one of two basic formats. The first is referred to as a leak rate test, in which the annulus between the inner and outer bellows plies is filled with a pressurized fluid, preferably air, from a remote pressure source. The goal is to maintain a specified, relatively constant pressure rating, such as 48 psi. The test measures the flow rate of pressurized fluid necessary to maintain the specified pressure. In the second test format, termed the pressure decay test, the annulus is pressurized to a specified value, and the decline of pressure over time is monitored and compared with optimum rates.
Basically, it has been found that in some cases, the plies of the bellows become crimped or pinched in random locations along the length of the bellows to the extend that the annulus between the inner and outer plies becomes completely closed, or restricts the flow of the pressurizing fluid. Should such a deformation occur upstream of an actual leak, the conventional pressure test scenarios will not discover the leak. Consequently, the nuclear regulatory establishment has been searching for an accurate system for leak rate testing of metallic expansion bellows.
Accordingly, it is a principal object of the present invention to provide an apparatus for accurately performing leak rate tests on pipe, and specifically, on sections of pipe equipped with metallic expansion bellows.
It is another object of the present invention to provide and apparatus for performing leak rate tests on pipe which also provides protection of the tested section of pipe from external damage.
It is yet another object of the present invention to provide an apparatus for performing leak rate tests on pipe which may be readily removed after testing and reused at another test sits.
It is a further object of the present invention to provide an apparatus for performing leak rate tests on pipe which may be left permanently installed after testing but still allow for easy access to the encompassed pipe section through partial disassembly of the apparatus. At the same time, the apparatus is designed to absorb any movements of the encased pipe while offing minimal resistance to such movement.
It is still another object of the present invention to provide an apparatus for performing leak rate tests on metallic expansion bellows which is compatible with existing pressure testing equipment.